1. Field of the Invention
The present invention relates to a wired circuit forming board, to a wired circuit board, and to a thin metal layer forming method. More particularly, the present invention relates to a wired circuit forming board having a thin metal layer on an insulating layer, to a wired circuit board for which the wired circuit forming board is used, and to a thin metal layer forming method for forming the thin metal layer.
2. Description of the Prior Art
In recent years, in the field of the wired circuit board, density growth of the conductive pattern is demanded increasingly. In general, a subtractive process and an additive process are known as a patterning process of the conductive pattern. From the viewpoint of advantage of the additive process over the subtractive process in density growth, the additive process is widely used.
In the additive process, a thin metal layer is formed on an insulating layer of a resin film, such as a polyimide film, by sputtering and the like and, then, a conductive pattern is formed on the thin metal layer by electrolytic copper plating.
In this additive process, it is known that for the purpose of providing improved adhesion between the insulating layer and the conductive pattern, a thin nickel layer having good adhesion with the insulating layer is formed on the insulating layer by sputtering, first, and, then, a thin copper layer having good adhesion with the thin nickel layer and the conductive pattern is formed on the thin nickel layer by sputtering.
Also, there is proposed a flexible printed wired circuit board wherein for example a metallized layer is formed on either a single side or both sides of a plastic film and a conductive metal layer laminated on the metallized layer by electroplating, the metallized layer comprising a layer consisting primarily of Ni and Cr and a layer consisting primarily of copper, and wherein composition in an area (interface area A) in the vicinity of an interface of the layer consisting primarily of Ni and Cr on the side thereof contacting with the plastic film and composition in an area (interface area B) in the vicinity of an interface of the layer consisting primarily of Ni and Cr on the side thereof contacting with the layer consisting primarily of copper are different from each other, and the Cr content in the interface area A is higher than the Cr content in the interface area B (Cf. JP Laid-open (Unexamined) Patent Publication No. 2003-318533, for example).
This JP Laid-open (Unexamined) Patent Publication No. 2003-318533 describes that this invention can produce a flexible printed wired board, such as an FPC board and a COF board, having good adhesion to prevent peel and delamination even after subjected to several processes of e.g. pattern forming, etching, wiring, and IC-mounting and then subjected further to severe environmental tests.
However, when the thin nickel layer and the thin copper layer are formed in sequence by sputtering, an interface is produced between the thin nickel layer and the thin copper layer. Likewise, in the invention of this publication (JP Laid-open (Unexamined) Patent Publication No. 2003-318533 cited above), the interface is produced between the layer consisting primarily of Ni and Cr and the layer consisting primarily of copper.
When this interface is produced between those two layers, the adhesion between those layers is reduced in the interface area in the subsequent process of, for example, plating the conductive pattern. Thus, even when the adhesion between the insulating layer and the conductive pattern is in good condition, delamination is generated in the thin metal layer due to the presence of the interface, causing the delamination of the conductive pattern.